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SubjectRe: [PATCH 2/3] make kernel threads invisible to /sbin/init
Quoting Oleg Nesterov (oleg@tv-sign.ru):
> 1. rename reparent_to_init() to reparent_kthread() and export it
>
> 2. use init_pid_ns.child_reaper instead of child_reaper(current)

Each of these patches looks good to me, but this part in particular
is a must-have bugfix.

Just started some tests, if any failures come back I'll report them
tonight.

thanks Oleg,
-serge

> 3. set ->exit_signal = -1, so init can't see us and we don't use
> it to reap the task.
>
> 4. add reparent_kthread() to kthread() and stopmachine()
>
> See also
>
> http://marc.info/?t=117580282200003&r=1
> http://marc.info/?t=95299284800003&r=1
>
> Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
>
> include/linux/sched.h | 1 +
> kernel/exit.c | 16 ++++++++--------
> kernel/kthread.c | 1 +
> kernel/stop_machine.c | 1 +
> 4 files changed, 11 insertions(+), 8 deletions(-)
>
> --- 2.6.21-rc5/include/linux/sched.h~2_DETACH 2007-04-05 12:18:28.000000000 +0400
> +++ 2.6.21-rc5/include/linux/sched.h 2007-04-10 21:52:27.000000000 +0400
> @@ -1401,6 +1401,7 @@ extern void exit_itimers(struct signal_s
>
> extern NORET_TYPE void do_group_exit(int);
>
> +extern void reparent_kthread(void);
> extern void daemonize(const char *, ...);
> extern int allow_signal(int);
> extern int disallow_signal(int);
> --- 2.6.21-rc5/kernel/exit.c~2_DETACH 2007-04-10 21:32:44.000000000 +0400
> +++ 2.6.21-rc5/kernel/exit.c 2007-04-10 21:59:41.000000000 +0400
> @@ -255,7 +255,7 @@ static int has_stopped_jobs(struct pid *
> }
>
> /**
> - * reparent_to_init - Reparent the calling kernel thread to the init task of the pid space that the thread belongs to.
> + * reparent_kthread - Reparent the calling kernel thread to the init task of the pid space that the thread belongs to.
> *
> * If a kernel thread is launched as a result of a system call, or if
> * it ever exits, it should generally reparent itself to init so that
> @@ -264,20 +264,20 @@ static int has_stopped_jobs(struct pid *
> * The various task state such as scheduling policy and priority may have
> * been inherited from a user process, so we reset them to sane values here.
> *
> - * NOTE that reparent_to_init() gives the caller full capabilities.
> + * NOTE that reparent_kthread() gives the caller full capabilities.
> */
> -static void reparent_to_init(void)
> +void reparent_kthread(void)
> {
> write_lock_irq(&tasklist_lock);
>
> ptrace_unlink(current);
> remove_parent(current);
> - current->parent = child_reaper(current);
> - current->real_parent = child_reaper(current);
> + current->parent = init_pid_ns.child_reaper;
> + current->real_parent = current->parent;
> add_parent(current);
>
> - /* Set the exit signal to SIGCHLD so we signal init on exit */
> - current->exit_signal = SIGCHLD;
> + /* make the task auto-reap */
> + current->exit_signal = -1;
>
> security_task_reparent_to_init(current);
> write_unlock_irq(&tasklist_lock);
> @@ -391,7 +391,7 @@ void daemonize(const char *name, ...)
> current->files = init_task.files;
> atomic_inc(&current->files->count);
>
> - reparent_to_init();
> + reparent_kthread();
>
> if (!has_rt_policy(current) && (task_nice(current) < 0))
> set_user_nice(current, 0);
> --- 2.6.21-rc5/kernel/kthread.c~2_DETACH 2007-04-05 12:18:28.000000000 +0400
> +++ 2.6.21-rc5/kernel/kthread.c 2007-04-10 22:02:31.000000000 +0400
> @@ -82,6 +82,7 @@ static int kthread(void *_create)
> sigset_t blocked;
> int ret = -EINTR;
>
> + reparent_kthread();
> kthread_exit_files();
>
> /* Copy data: it's on keventd's stack */
> --- 2.6.21-rc5/kernel/stop_machine.c~2_DETACH 2006-10-22 18:24:03.000000000 +0400
> +++ 2.6.21-rc5/kernel/stop_machine.c 2007-04-10 22:04:23.000000000 +0400
> @@ -33,6 +33,7 @@ static int stopmachine(void *cpu)
> int irqs_disabled = 0;
> int prepared = 0;
>
> + reparent_kthread();
> set_cpus_allowed(current, cpumask_of_cpu((int)(long)cpu));
>
> /* Ack: we are alive */
-
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